The publications resulting from our activities of the past year are listed in the accompanying bibliography. They demonstrate our interest in specific signaling molecules that allow neurons to communicate with one another in highly specific ways that are experience-dependent, and allow behavioral plasticity and adaptability. For example, we have mapped the hypothalamic hormone vasopressin to nerve terminals at new locations in the brain (e.g. lateral habenula) using single-cell labeling of the cell bodies of these neurons at their source in the paraventricular nucleus of hypothalamus, and characterized co-expressed transmitters and enzymes, including the aromatase that converts testosterone to estrogen in the brain. These neurochemical characterizations have been used to demonstrate that in gonadectomized mice, the vasopressin projections to lateral habenula are lost, as is corresponding activation of LHb neurons after stress. Hormone replacement therapy (testosterone treatment) restores both behavioral effects and vasopressin projections to Lab, suggesting that this projection system exerts actions on animal responses to rewarding and aversive stimuli in a sex steroid (gonadal status)-dependent way (Zhang et al., 2018). We have also identified co-expression of inhibitory and excitatory neurotransmitter markers in neurons that contain the stress-associated peptide PACAP in rodent brain, suggesting that co-transmission is an underlying mechanism for PACAP actions on stress-induced relapse to drug-seeking behaviors, as well as stress-induced depresssogenic behaviors that are PACAP-dependent (i.e. are abrogated in PACAP-deficient mice). With our colleagues at the University of Marburg, the University of Illinois, and the Autonomous National University of Mexico (UNAM) we have shown (Zhang, Gillette, Weihe and Eiden, in preparation) that glutamate co-release with PACAP in the suprachiasmatic nucleus (SCN) of the hypothalamus is responsible for light-induced (mimicked by glutamate administration in ex vivo SCN preparations) phase shifts in the level of activation of this nucleus, relevant to cooperation between two transmitters-- peptide and an excitatory amino acid--in mediating behavioral plasticity associated with seasonal adaptation in the mouse. In other work, we have determined a mechanism, receptor-specific desensitization, to explain how G-protein coupled receptors for biogenic amines and neuropeptides can differentially activate a neuronal-specific pathway to MAP kinase activation in neuroendocrine cells through the neuronally-expressed guanine nucleotide exchange factor NCS-Rapgef2 (Jiang et al., eNeuro, 2017). This pathway is required (i.e. activation is abrogated by down-regulation of NCS-Rapgef2) for ERK activation in response to cocaine or amphetamine in D1 dopaminoceptive neurons of the nucleus accumbens, a critical center for reward and addiction in the brain. Our results further predict that In the brain stimulation of beta-1 adrenergic receptors by norepinephrine (as for D1 receptors by dopamine) activates the neuronal MAP kinase ERK, while stimulation of beta-2 adrenergic receptors by norepinephrine does not activate this pathway. Activation of the neuronal ERK pathway in dopamine-responsive neurons allows the expression of neuronal plasticity (incorporation of experience into altered circuit properties and emergent behaviors) in rodents, including locomotor sensitization to cocaine and preference for cocaine imbibition, a surrogate for cocaine dependence. We are currently verifying the effects of NCS-Rapgef2 inhibition in nucleus accumbens on these behaviors associated with cocaine ingestion. If successful, we will extend this work to examination of differential effects of beta-1 and beta-2 receptor activation on norepinephrine-dependent behaviors in other brain regions. Finally, we have begun a multi-year and difficult project, but one as yet unassayed by other laboratories, to causally link changes in the morphology of neuronal dendrites-- changes in shape and number of dendritic spines--to specific behaviors including psychomotor stimulant drug dependence.